Measurement of CP violation at a Neutrino Factory

The prospects of measuring CP violation in the leptonic sector using the intense neutrino beams arising from muon decay in the straight sections of a muon accumulator ring (the so-called neutrino factory) are discussed.Comment: Invited talk given at the CP2000 Conference in Ferrara, September, 200

The Three Neutrino Scenario

I have discussed in my talk several remaining issues in the standard three-flavor mixing scheme of neutrinos, in particilar, the sign of $\Delta m^2_{13}$ and the leptonic CP violating phase. In this report I focus on two topics: (1) supernova method for determining the former sign, and (2) illuminating how one can detect the signatures for both of them in long-baseline (\gsim 10 km) neutrino oscillation experiments. I do this by formulating perturbative frameworks appropriate for the two typical options of such experiments, the high energy and the low energy options with beam energies of $\sim$ 10 GeV and $\sim$ 100 MeV, respectively.Comment: 6 pages, Latex, 2 figures. Talk presented at Europhysics Neutrino Oscillation Workshop (NOW2000), Otranto, Italy, September 9-16, 200

CP Trajectory Diagram; A tool for pictorial representation of CP and matter effects in neutrino oscillations

We introduce "CP trajectory diagram in bi-probability space" as a powerful tool for pictorial representation of the genuine CP and the matter effects in neutrino oscillations. Existence of the correlated ambiguity in a determination of CP violating phase \delta and the sign of \Delta m^2_{13} is uncovered. Principles of tuning beam energy for a given baseline distance are proposed to resolve the ambiguity and to maximize the CP-odd effect. We finally point out, quite contrary to what is usually believed, that the ambiguity may be resolved with 50 % chance in the super-JHF experiment despite its relatively short baseline of 300 km.Comment: 6 pages with 2 postscript figures. Talk presented at The 3rd International Workshop on Neutrino Factories Based on Muon Storage Rings (NuFACT01), Tsukuba, Japan, May 24-30, 200

Natural Mass Generation for the Sterile Neutrino

We point out that there is a serious cosmological problem in the supersymmetric standard model if a sterile neutrino is responsible for the solar neutrino oscillation, and propose a possible solution to this problem. We show that our solution induces naturally a mass of order 10^{-4} eV for the sterile neutrino, which is deeply related to the mechanism of supersymmetry breaking.Comment: 8 pages, no figures, minor changes, reference adde

Electronic and magnetic influences of a stacking fault in cobalt nanoscale islands on the Ag(111) surface

Utilizing spin-polarized scanning tunneling microscopy and spectroscopy, we found coexistence of perpendicularly and in-plane magnetized cobalt nanoscale islands on the Ag(111) surface, and the relationship between the moire corrugation amplitude and the magnetization direction of the islands; the islands with the stronger moire corrugation show the perpendicular magnetization, and the ones with the weaker moire corrugation do the in-plane. Density functional theory calculations reproduce the relationship and explain the differences between the two types of the islands with an fcc stacking fault in the intrinsic hcp stacking of cobalt.Comment: 8 pages, 8 figure

Measuring Leptonic CP Violation by Low Energy Neutrino Oscillation Experiments

We uncover an interesting phenomenon that neutrino flavor transformation in slowly varying matter density imitates almost exactly that of vacuum neutrino oscillation under suitably chosen experimental parameters. It allows us to have relatively large CP violating measure \Delta P \equiv P(\nu_{\mu} \to \nu_e) - P(\bar{\nu}_{\mu} \to \bar{\nu}_e) which is essentially free from matter effect contamination. We utilize this phenomenon to design a low-energy long-baseline neutrino oscillation experiment to measure the leptonic CP violating phase.Comment: RevTex file, 13 pages, 2 postscript figures, revised version, some new discussions were added, Fig. 2 was replace

On suppressing the Higgsino-mediated proton decay in SUSY SO(10) GUT's

Using the freedom in SO(10) GUT's one can generalize the existing models without changing the mass spectrum of fermions to obtain a significant suppression of proton decay resulting from the baryon number violating operators of dimension 5. In some limiting cases, their contributions can be made negligible compared to the dimension 6 operators resulting from the heavy gauge bosons exchange.Comment: 19 pages, 3 Postscript figures, 2 mpost figures, rearranged plots, corrected typo